Dog Psychology

Our mutt Goldie, AKA Goldman, Golden Boy, etc., loves our daily walk. We take pretty much the same route and he reacts pretty much the same way when other dogs are around. If they're on a leash, he goes absolutely berserk, barking, pulling and generally being obnoxious. I need to cross to the other side of the street. But here's the funny part: If the other dog is not on a leash, Goldie's docile as can be.

Case in point: There's this beautiful chocolate lab who's always loose in his yard, thanks to the electronic fence his owners installed. When we come down the sidewalk directly through his yard, the chocolate stands to attention, barks a few low hellos, wagging his tail the whole time. Goldman, on the other hand, neither barks nor looks in the chocolate's direction as he saunters by. Never. Goldie acts as if there is nothing there at all.

So what is going on here? Why berserk one minute and indifferent the next? He never deviates from this behavior. I would love to hear some theories.